Embodiments of the present invention relate to a method of removing a low-k dielectric layer from a wafer to refresh the wafer.
In the processing of substrates, such as semiconducting wafers and displays, a test wafer is often used to determine processing uniformity. During processing, a substrate is placed in a process chamber and suitable processing conditions are maintained in the chamber. Processing of the substrate can involve, for example, energizing a process gas to etch the substrate or deposit material on the substrate. The substrates are typically processed in a series of processing steps to form a final substrate product, which may be an integrated circuit having metal interconnect metal layers with dielectric material in between. To evaluate the results from one or more of the processing steps, a test wafer can be processed in the chamber in place of the production substrate. The test wafer can be processed to determine processing results such as the deposited film thickness uniformity and particle counts, and the process parameters can be modified according to the test results to provide improved processing performance. For example, for a deposition process, the test wafer may be processed to determine a thickness uniformity, composition and wafer stress of a deposited film.
In one testing method, test wafers are used to evaluate processing of a low-k dielectric material on a substrate. Low-k dielectric materials have a dielectric constant “k” that is lower than conventional dielectric materials, such as silicon oxide, and may typically have a ‘k’ value of less than about 3. Examples of low-k dielectric materials can comprise compositions of silicon, oxygen and carbon, and even hydrogen, such as for example, the “Black Diamond™” dielectric material, and such materials may be formed by a chemical vapor deposition method. Low-k dielectric layers can reduce an RC delay time in an integrated circuit, allowing corresponding increases in metal interconnect density. Accordingly, the formation of low-k dielectric layers having properties that meet the processing specification is important for the fabrication of high-density circuits, especially for circuits having feature sizes of less than about 100 nm.
After testing, the wafers used to evaluate low-k dielectric layer deposition processes can be refreshed, by removing the low-k layer and refurbishing the test wafer for subsequent process evaluations. Refreshing and reclamation of test wafers is desirable to cut down on the cost of providing fresh test wafer materials. Refreshing may also be a suitable method of reusing production wafers with low-k dielectric layers that were poorly processed. In one version, a wafer having a low-k dielectric layer is reclaimed by mechanically grinding the low-k dielectric material off the wafer, for example with a grinding wheel. In another version, a chemical solution is used to remove the material.
However, standard refreshing techniques often fail to suitably remove low-k dielectric materials. For instance, some low-k dielectric materials are difficult to remove chemically, as the combination of organic and inorganic elements renders the material less reactive with many chemical compositions, and many chemical compositions can convert the low-k dielectric material into a gummy residue on the wafer. Also, conventional means such as grinding can excessively scratch and otherwise damage the wafer surface. Surface damage can undesirably affect the deposition of a low-k dielectric layer on the surface, and alter the deposition testing results. As such, conventionally reclaimed wafers are often only suitable as mechanical-grade testing wafers, for example, for mechanical robot testing to evaluate wafer positioning, but may not be suitable as test-grade wafers for evaluating substrate processes. The conventional refreshing methods may also erode away an excessive amount of the wafer during the low-k removal process. This excessive erosion can limit the number of times the wafer can be reclaimed for re-use, before disposal of the wafer becomes necessary. Accordingly, conventional refreshing techniques do not always provide satisfactory removal of low-k dielectric materials to allow re-use of the wafers.
Thus, it is desirable to be able to reclaim a wafer having a low-k dielectric material. It is furthermore desirable to be able to refresh a test wafer to remove a low-k dielectric layer, to provide a fresh test wafer for testing low-k dielectric layer deposition processes. It is further desirable to completely remove residual low-k dielectric material from the test wafer in the refreshing process.